As shown in FIG. 5, the hitherto known conventional surface area measuring apparatus for particulate materials generally comprises a first conduit 1, a second conduit 2 and a third conduit 3; a gas meter means A interposed midway in the first conduit 1; another gas meter means B interposed midway in the third conduit 3; a first U-shaped sample cell 4 detachably connected to the terminal of the first conduit 1 at one end thereof and also detachably connected to the starting point of the second conduit 2 at the other end thereof; and a second sample cell detachably connected to the terminal of the second conduit 2 at one end thereof and also detachably connected to the starting point of a third conduit 3 at the other end thereof.
The surface area of a sample is measured by such an apparatus in the following manner.
The sample is placed in the second sample cell 5 and the cell is connected to the terminal of the second conduit 2 and the starting point of the third conduit. The first sample cell 4 is also connected to the terminal of the first conduit 1 and the starting point of the second conduit 2. Then the second sample cell is heated to a high temperature and a deaerating gas is passed through the first conduit, the first sample cell, the second conduit, the second sample cell and the third conduit and thereby slight amounts of moisture and adsorbed gases in the sample in the second sample cell 5 are removed. After this deaeration has been continued for a predetermined period of time, the two sample cells are detached from the conduit line, the second sample cell 5 is connected to the terminal end of the first conduit at one end and to the starting end of the second conduit 2 at the other end and the first sample cell is connected to the terminal of the second conduit 2 at one end and to the starting point of the third conduit 3 at the other end. Thereafter, a measuring gas, which is a mixture of an inert gas and nitrogen, is passed through the first conduit 1, the second sample cell 5, the second conduit 2, the first sample cell 4 and the third conduit 3 while the second sample cell 5 is chilled with liquid nitrogen so that the nitrogen is adsorbed on the sample.
While this operation is being carried out, the gas flow detected at the gas meter means A is larger than that detected at the gas meter means B. When the sample is saturated with the nitrogen, the gas flows detected by the gas meter means A and the gas meter means B become equal. Then chilling of the second sample cell 5 is discontinued while the flow of the gas mixture is maintained and the temperature of the second sample cell returns to room temperature.
As the temperature of the second sample cell rises, the adsorbed nitrogen is gradually desorbed and the gas flow detected at the gas meter means B becomes larger than that detected at the gas meter means A. The amount of the adsorbed nitrogen can be measured by integrating the increasing gas flow.
The surface area of the sample can be calculated from the amount of the adsorbed nitrogen.
With a surface area measuring apparatus of this structure, exchange of the first sample cell 4 and the second sample cell 5 in the conduit system is necessary.
The reason why the first sample cell 4 and the second sample cell 5 must be exchanged is that a heating means and a chilling means are required.
In order to make the apparatus a closed system, the first sample cell 4 is required in addition to the second sample cell 5. This increases the number of apparatus parts and makes the operation more complicated.
Therefore, a surface area measuring apparatus, which does not require surplus parts such as the first sample cell 4 as shown in FIG. 6, is known.
In this apparatus as shown in FIG. 6, a conduit 6 for deaerating gas is connected to a three-way valve 7; a conduit 8 for measuring gas is connected to the three-way valve 7 via a first gas meter means A and a second three-way valve 9; the remaining outlet of the first three-way valve 7 is communicated to the inlet of the sample cell 11 via conduit 10; the outlet of the sample cell 11 is communicated to another three-way valve 13 via a conduit 12: one outlet of the third three-way valve 13 is communicated to a first exhaust conduit 14; the remaining outlet of the third three-way valve 13 is communicated to a fourth three-way valve 15 and to a second exhaust conduit 16 via a fourth three-way valve 15 and another gas meter means B; the second three-way valve 9 and the fourth three-way valve 15 are communicated to each other by means of the remaining outlets via a conduit 17.
When deaeration is carried out with this apparatus, the ports (1) and (2) of the first three-way valve 7 are communicated, the ports (2) and (3) of the second three-way valve 9 are communicated, the ports (1) and (2) of the third three-way valve 13 are communicated and the ports (3) and (1) of the fourth three-way valve 15 are communicated, and thus a passage is formed from the conduit 6 for deaeration gas to the exhaust conduit 14 via the three-way valve 7(1)(2), the sample cell, the three-way valve 13(1)(2).
A deaeration gas is passed through the sample cell 11 which contains a sample, while the measuring gas is passed through the first gas meter means A, the second three-way valve 9(2)(3), the conduit 17, the fourth three-way valve 15(3)(1), the second gas meter means B and the exhaust conduit 16.
After the deaeration is finished, the three-way valves 7, 9, 13 and 15 are switched over so that the measuring gas passes through the first gas meter means A, the second three-way valve 9(2)(1), the first three-way valve 7(3)(2), the sample cell 11, the third three-way valve 13(1)(3), the fourth three-way valve (2)(1), the second gas meter means B and the exhaust conduit 16.
In an apparatus, in which a plurality of three-way valves are employed, however, the switch-over of the three way valves is complicated and troublesome and the operation of such an apparatus is apt to be accompanied by danger of operation error.
Further, conventional surface area measuring apparatuses are not free from gas leakage at the part where the sample cell is mounted. In other words, in conventional apparatuses, perfect mounting of the sample cell is not easy.